Gas-liquid contactors are widely used in many industries such as chemical, biochemical, petrochemical and metallurgical industries. The selection, design, sizing and performance of these contactors or reactors often depend on the mass and heat transfer, hydrodynamics, and reaction kinetics. These units are commonly encountered as aerators or gas-liquid reactors, where the gas first dissolves in the liquid and then reacts with the liquid or any materials dissolved in the liquid. The reactions in such reactors are often classified into slow and fast regimes (Advances in Chemical Engineering, Academic Press 1981, pp. 1-133). For slow reactions, high liquid holdup and mass transfer are needed to maintain the gas concentration in the bulk close to the saturation, while for fast reactions, high gas holdup and small bubble size are required since the gas concentration in the liquid bulk is almost zero and the gas-liquid interfacial area controls the rate of gas absorption (Advances in Chemical Engineering, Academic Press 1981, pp. 1-133). By increasing the contact surface area between the gas and the liquid, faster chemical or biochemical reaction rates will be achieved and correspondingly higher mass transfer rates.
One major drawback of some high performance gas-liquid contactors that involve good mixing is the need for high mechanical energy. However, such mechanical energy may be utilized more efficiently in some types of gas-liquid contactors than others. The mass transfer performance of different gas-liquid contactors under the same operating conditions may thus vary significantly (Chemical Engineering and Processing: Process Intensification, 38 (1999) 503-510). Bubble column reactors, spouted bed rectors, packed columns and agitated reactors with high liquid holdup are suitable for slow-reaction processes such as liquid-phase oxidations, hydrogenations, chlorination and some fermentation (Advances in Chemical Engineering, Academic Press 1981, pp. 1-133). Plate, packed columns and venturi-type reactors are more suitable for fast reaction processes due to the high gas-liquid interfacial area (Chemical Engineering Science, 48 (1993) 889-911); however, under specific conditions, bubble column reactors and packed column reactors are suitable for highly exothermic fast reaction processes, which are widely used in the chemical, biochemical, petrochemical and metallurgical applications (Chemical Engineering Science, 48 (1993) 889-911).
Gas-liquid contactors may be classified into surface and volume contactors. They may also be sorted based on the level of mass transfer rate inside the apparatus. Contactors with low mechanical energy consumption have in general low mass transfer rates and low performance. More mechanical energy consumption, which is usually associated with more mixing, inside a gas-liquid contactor improves the mass transfer rate. Such gas-liquid contactors are called high performance contactors and they become important with increasing demand for high gas absorption rates and for small volumes of the installed equipment (Chemical Engineering and Processing: Process Intensification, 38 (1999) 503-510).
Surface gas-liquid contactors are typically used for biological wastewater treatment and usually have the form of pools with moderately low depth. They often involve the use of impellers or liquid jets to create the required gas-liquid interfacial area (Chemical Engineering and Processing: Process Intensification, 38 (1999) 503-510). On the other hand, in volume gas-liquid contactors, the interfacial area between the gas and liquid phases is created within the bulk of the liquid. The gas phase is dispersed in the form of bubbles with spherical or irregular shape. Gas dispersion in the liquid is usually achieved through the use of spargers, liquid jets, two-mixture nozzles or hollow rotating mixers (Chemical Engineering and Processing: Process Intensification, 38 (1999) 503-510). Examples of common gas-liquid contactors/reactors include bubble column reactors, stirred vessel reactors, jet loop reactors, reciprocating jet reactors, and impinging-stream reactors. A bubble column reactor is a vessel in which a sparger is placed at the bottom and it is characterized by relatively low mass transfer performance.
Bubble columns are generally used in the bio-processing industry to perform a range of aerobic fermentations due to their mechanical simplicity, low capital cost, and good heat and mass transfer characteristics (Chemical Engineering Journal, 264 (2015) 291-301). The volumetric mass transfer coefficient value in a bubble column depends on the physical properties of the fluids used, the gas flow rate (Chemical Engineering and Processing: Process Intensification, 38 (1999) 503-510), sparger design (Chemical Engineering and Processing: Process Intensification, 38 (1999) 329-344), reactor length to diameter ratio (H/D) (Chemical Engineering Science, 25 (1970) 340-341), system pressure (Chemical Engineering Science, 52 (1997) 4447-4459), and temperature (Chemical Engineering Science, 56 (2001) 6241-6247). The bubble size inside the bubble column approaches a stable size shortly after dispersion. Under such conditions, the mass transfer performance becomes less sensitive to the design of the sparger (Chemical Engineering Science, 48 (1993) 889-911).
The advantages of bubble column rectors are: low maintenance and operating cost, low capital, excellent heat transfer and temperature control, high gas-liquid interfacial area and volumetric mass transfer coefficient at low energy input and high liquid volume and residence time due to the reactor geometry and height to diameter ratio. These reactors do, however, suffer from some drawbacks such as back-mixing and bubble-bubble interactions in the churn-turbulent flow regime; difficult catalyst and liquid separation, particularly for highly viscous slurries containing fine particles; and complex scale-up due to the lack of knowledge on the hydrodynamics and mass transfer characteristics under typical industrial conditions (Fuel Processing Technology, 89 (2008) 322-343).
A stirred vessel reactor is usually a cylindrical vessel equipped with an impeller at its center. A sparger is placed under the impeller to enhance mixing and mass transfer through introducing small gas bubbles with a high surface area per unit volume and through increasing the level of turbulence in the liquid (Chemical Engineering Science, 92, (2014) 2191-2200). A jet loop reactor, on the other hand, is a vessel fitted with a two-mixture nozzle and a draft tube. The nozzle may be fixed at the top or at the bottom of the reactor and the draft tube may be either concentric with the main tube or next to it. The liquid jet at the nozzle outlet makes gas dispersion with very small size bubbles. The liquid momentum leads to circulation of the gas-liquid mixture, which leads to good mixing in these type of reactors with no dead zones (Chinese Chemical Engineering, 22 (2014) 611-621).
The reciprocating jet reactor consists of a number of perforated discs connected together with a central shaft. The discs and the shaft are placed in a cylindrical vessel and receive a counter motion with high amplitude and a frequency, causing the mixture to flow through the holes of the discs in the form of jets (Chemical Engineering and Processing: Process Intensification, 38 (1999) 503-510). Gas and liquid are fed to the reactor through nozzles placed at the inlet of guide tubes. A homogeneous two-phase stream is formed. The gas phase is dispersed and the kinetic energy of the two-phase streams is dissipated. This creates a high turbulence and a large mass transfer area between the gas and the liquid phase (Chemical Engineering Science, 47, (1992) 2877-2882).
Although the above-mentioned gas-liquid contactors have been widely used in many industries, none of them can be applied to a variety of unit operations with the same efficiency, and they all suffer from different drawbacks such as complexity, high demand for mechanical energy and difficulty to scale-up. The current invention describes a simple system that can provide excellent gas-liquid contact, high performance efficiency and can be easily scaled-up.